The present invention relates generally to retractable steps for assisting in entering or exiting construction equipment cabs, vehicles or the like, and more particularly, to a locking step that is manually pulled to an extended, or operative position from a retracted position under a cab.
Steps or ladders for assisting in entering and exiting vehicles are well-known in the art. In the past, these steps or ladders typically extended outwardly and depend downwardly from under the vehicle door. In some instances involving construction equipment without width restrictions, these steps are permanently fixed in an operative position. While such arrangements are also suitable for use on some other types of vehicles, such as passenger vans or truck cabs, construction vehicles with width restrictions require a different approach. For example, truck mounted cranes typically have operator cabs positioned on a rotating turntable or upper works that is mounted to the deck or lower works. To enter the cab, the crane operator must climb directly from the deck through the cab door. This climb is made difficult by the fact that the cab is substantially elevated above the deck and the cab door faces the side of vehicle. Since the entry side of the cab is often extending out only as far as the edge of the deck, which commonly is at or near the maximum width permitted for over-the-road vehicles under federal, state, and local regulations, this means that there is no deck space to step on when the operator is entering or exiting the cab with the boom extending directly forward or rearward. The use of a fixed step that extends outwardly from the cab is not permitted since it would increase the vehicle width beyond what is allowed by these regulations.
Lessening the width of the cab or the upper frame accommodate a fixed step is generally not an option. In most truck mounted cranes, the width of the carrier deck is made as wide as possible to provide greater crane stability. Also, all available space in and under the cab is needed for hydraulic plumbing, controls and other necessary operating mechanisms.
The comfort for the operator is also a concern. Thus, while the cab width is maximized to provide the necessary room for the mechanical equipment, it is imperative at the same time to provide the proper attention to operator ergonomics. All of this has to be accommodated without exceeding the width of the carrier deck.
The alternative of a fixed step that projects forwardly and outwardly is a ladder that depends directly down from the edge of the cab. Although such a ladder does not significantly add to the vehicle width, it is not suitable for use on a truck mounted crane. The fixed step or ladder may interfere with the deck, or structures on the deck, required for operation of the boom as the turntable and cab rotate. It is also difficult to access from the side, as indicated above.
Others in the past have proposed retractable steps that can be stored under the vehicle or cab and extended to an operative position. An example is found in U.S. Pat. No. 5,342,073 to Poole, which discloses a retractable step that is mounted on the underside of a passenger van. The step is provided with side support tubes that slide on horizontally extending cross guides. This arrangement permits the step to move horizontally between the retracted and extended positions. Plates at the inner ends of the support tubes trap the step adjacent the end of outward, extended travel to prevent inadvertent removal.
One disadvantage of the arrangement proposed in the ""073 patent is that the step is held in the retracted position only by thin, spaced stops formed on the support tubes. If the vehicle carrying the retractable step is subjected to significant vertical jarring, such as is created when potholes, speed bumps, or the like are encountered, the step can inadvertently move into the extended position Of course, this lack of a positive locking arrangement suggests having to use stop gap measures, such as the use of a bungee cord or the like to hold the step in place.
Another disadvantage is that there is no lateral stability in the ""073 design. Indeed, the step is intended for use by people entering only over the outer or front edge. Stepping on the side of the step would likely cause sudden sidewise shifting along the cross guides. This, in turn, could lead to a sudden loss of balance of the person using the step.
Other types of folding or retractable steps have also been proposed, but most of these have a large number of component parts, and are also actually restricted to use for entry over the outer or front edge. This is so since the part of the operating mechanism extends above the tread on the sides of the step providing direct foot interference; see, for example, U.S. Pat. No. 3,955,827 to Wonigar. Still others require relatively long and thin depending support arms and slotted levers that are also subject to sudden shifting or swinging, and thus also the risk of loss of balance when stepping onto the side of the tread of the step. Also, the arms and levers are subject to bending and over time becoming jammed rendering the step inoperative; see U.S. Pat. No. 5,284,349 to Bruns et al.
Accordingly, a need is identified for a retractable step that can be manually extended from under a vehicle, crane or excavator cab, or the like. In the operative position, the step would extend substantially in the horizontal plane, have a very low profile and be stable for side entry onto the tread, thus making it suitable for use with a cab mounted on a turntable supported on a truck chassis. To hold the step in both the extended and retracted positions, a manually operable mechanism would be provided to securely lock the step in place. The step would also be simple in design and inexpensive to manufacture. Ease of installation would allow the step to be retrofitted onto existing cabs or other desired locations without significant time or effort. Overall, the locking retractable step would result in an improvement in stability and reliability over those known in the art, and would be particularly adapted for use on crane/excavator cabs or the like.
Accordingly, it is a primary object of the present invention to provide an improved step assembly. for mounting under a crane cab or other vehicle, and wherein the step can be manually pulled from a retracted position to an extended, operative position for assisting in climbing into or out of the cab from any direction.
Another object is to provide a pull out step assembly including a step that has a low profile and moves substantially horizontally to an extended position, such that during rotation of the crane cab, it does not interfere with existing structures required for operation of the crane.
Still another object of the present invention is to provide a pull out step assembly that includes a positive locking mechanism for holding the step securely in place in both the extended and retracted positions.
Still another object of the present invention is to provide a pull out step assembly that incorporates a step that is inherently stable to permit stepping on the side of the tread, as required by entry or exit of some cranes or the like.
Yet another object of the present invention is to provide a pull out step assembly that is inexpensive to manufacture, and sturdy and reliable in use.
A further object of the present invention is to provide a pull out step assembly that is simple to install and easily retrofitted onto locations where a retractable step is desired without extensive modification to the existing structure.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, an improved pull out step assembly is mounted under the cab of a crane or excavator, and is manually extendable to an operative position for assisting in climbing into or out of the cab. The step assembly has a low profile when mounted under the cab, and the step extends substantially horizontally to an extended position so as to avoid interfering with the rotation of the crane cab.
Advantageously, the step assembly also includes a built-in, manually operable locking mechanism that positively secures the step in place in both the extended and retracted position. Moreover, the step is designed to be stable when the tread is stepped on from the side. Lateral shifting of the step is prevented due to the unique design of the retracting mechanism.
Furthermore, the step assembly is relatively simple in construction and is easily retrofitted onto existing crane cabs. Although the step assembly is described as being particularly adapted for use on the cab of a crane, excavator or similar location, it should be appreciated that it is possible to adapt the invention described herein for use on other types of vehicles or any other locations where a retractable step, particularly with lateral stability, may be desirable.
In the broadest aspects of the invention, the locking cab step assembly includes a pair of elongated L-shaped brackets for mounting to the underside of a cab or the like. The brackets are provided with opposed forward and rearward slots for receiving the ends of laterally extending locking rods. Upon engagement with the appropriate pair of the forward/rearward slots, the step is held in place in a positive, secure manner in either the extended or retracted positions, respectively.
The step is mounted between support guides, such as C-shaped channel members, that embrace pairs of side support rollers on the brackets that permit the step to move in and out in the horizontal plane, but advantageously prevent lateral shifting during use. This mounting allows the step to be pulled from the retracted to the extended position for use in assisting in entering or exiting the cab and returned to the retracted position when not in use to comply with regulations on maximum vehicle width. When the operator steps on the tread from any direction, including from the side, the step remains secure and stable to insure the operator""s balance as the cab is entered or exited.
The locking mechanism, which also enhances the lateral stability, includes a pair of reciprocal locking rods that extend in a transverse direction relative to the C-shaped channel members of the step and the mounting brackets. To provide the desired locking function, the ends of the locking rods engage the rearward slots formed in the brackets when the step is in the retracted position and the forward slots when the step is in the extended, or operative position. Means for manually moving the reciprocal locking rods into and out of engagement with the respective pair of slots is also provided. Thus, as described further below, manually disengaging the reciprocal locking rods from the respective slots allows the step to freely move between the extended and retracted positions. The slots are also formed having an oversized vertical dimension to compensate for slight dimensional and operational variations between the channel members and the support rollers.
The C-shaped channel members on the sides of the step provide a three-sided bearing surface for contacting and fully embracing the support rollers. Thus, when the reciprocal locking rods are disengaged, the step can be manually pushed or pulled as the rollers rotate and the channel members move effortlessly in and out. The side faces of the rollers engage the cross web of the respective C-shaped channel member, thus embracing the channel members and preventing any deleterious lateral shifting that could cause a sudden loss of balance of the operator as the tread of the step is engaged from the side. A stop may be provided at the forward and rearward ends of both channel members to prevent the step from inadvertently becoming disengaged.
Also in the preferred embodiment, the reciprocal locking rods move into and out of engagement with the forward and rearward slots through use of a operating shaft extending toward the outer edge of the step. One or more reinforcing cross members extend along the underside of the step and provide bearing apertures for the operating shaft. A pivotal handle is provided at the proximal or outer end to rotate the shaft and is easily accessible from under the step. At the opposite or distal end of the operating shaft, a dual crank is provided that receives the ends of the reciprocal locking rods. Thus, as should be appreciated, turning the handle either clockwise or counterclockwise from a resting position rotates the dual crank, which in turn moves the ends of the locking rods out of engagement with the respective slots.
At least one of the locking rods is preferably provided with a biasing element, such as a compression spring, to force the rods in the direction of the respective bracket. Thus, once the rotary pressure on the handle is released after the rods are disengaged from the respective slots, the biasing force supplied by the compression spring lightly presses the rods against the inside face of the brackets. When the step is moved in either direction, such that the locking rods reach the slots, the rods automatically shift into engagement to securely lock the step in place. The step is then ready for use in climbing into the crane cab. Advantageously, because the step extends substantially horizontally and has a low profile, it can remain in the extended position during rotation of the crane cab without interfering with existing structures on the carrier deck. Only when movement to anotherjob site is required is it necessary to retract the step.
As should be appreciated, to retract the step, the handle is manually rotated such that the locking rods move inwardly and disengage from the forward slots. Once the slots are cleared, the rotary pressure exerted on the handle can be released. The step is then pushed inward by the handle with the ends of the locking rods riding along the support bracket. When the locking rods reach the rearward slots, the biasing force provided by the compression spring causes the rods to shift into engagement and hold the step securely in place in the retracted position.
Still other objects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of this invention, simply by way of illustration of one of the modes best suited to carry out the invention. As it will be realized, the invention is capable of other different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive.